Precise mixing of chemicals, particularly gases in liquids, has been a desire of the chemical industry. The semiconductor industry has sought precise dilutions or concentrations of chemical mixtures due to its demanding requirements for purity and concentration in the fabrication of semiconductor materials of construction.
U.S. Pat. Nos. 4,002,268; 5,332,125; 5,383,574 and 5,429,276 are directed to mixing of chemicals in general in the chemical industry.
U.S. Pat. Nos. 5,148,945; 5,330,072 and 5,417,346 are directed to mixing of chemicals in the chemical industry and more particularly precise mixing for the semiconductor industry.
U.S. Pat. Nos. 5,370,269 and 5,490,611 are relevant to precise mixing of chemicals for the chemical and semiconductor industry using metered vessels and constricted vent tubes with level sensors to achieve the precise mixing and dilution requirements of the semiconductor industry. Unfortunately, they suffer from slow mixing rates and false readings from the level sensors under desired mixing rates.
The present invention overcomes the drawbacks of the prior art to provide precise and accurate mixing, dilution and concentrations of chemicals at rapid rates and without false or premature signals from level sensors in a metered vessel using constricted vent tubes, as will be more fully set forth below.